This is a new application for an R01 grant, in response to RFA-DK-08-009, entitled: Neuroimaging studies of reward, impulsivity, and adherence to an exercise program. Obesity is the result of chronic imbalances between energy intake and expenditure. Regular exercise is a critical component of maintaining energy balance and it is associated with health benefits, including enhanced brain function. Health-related decisions are influenced by a convergence of processes in the brain, as individuals weigh the perceived balance between the rewarding and punishing aspects of the behavior, and whether gratification is immediate or delayed. Healthy behaviors, such as regular exercise, are in part difficult to maintain because they are less immediately gratifying. In fact, exercise may initially be perceived as aversive. Despite this challenge, some people are able to persevere and experience long-term benefits. We hypothesize that brain processes underlying reward processing and impulse control will help us better understand mechanisms of obesity and health-related decision making. We will scan sedentary obese and sedentary healthy weight (HW) participants with reward prediction and delay discounting fMRI paradigms before and after a nine-month exercise intervention. The study will address three Specific Aims: 1. Characterize brain activation underlying reward processing and impulse control in obese and healthy eight individuals. 2. Identify brain activation predictors, from the Baseline Session, of adherence and success in the exercise program. 3. Identify the beneficial effects of exercise and increased fitness on brain activation. We predict that measures of brain activation will be useful in identifying neural contributions to obesity, determinants of adherence to a long-term exercise program, and the beneficial effects of exercise on brain function.